The present invention relates generally to DC power supplies and, more particularly, to a power supply which provides a number of DC voltages of different levels, including a positive/negative balanced output for integrated circuit applications through the use of a transformer having a minimal number of secondary winding terminals.
Present day electronic equipment particularly solid state devices for carrying out a multitude of signal processing and control operations, typically require power supplies capable of providing more than one DC supply voltage for various loads, including the devices themselves, to be energized by the equipment. In equipment which carries out small signal amplification and processing in one area, and provides means for driving a relatively large power consuming device (e.g., a printer) in another area, a power supply capable of providing a balanced DC output of; for example, plus and minus 12 volts to a number of differential amplifiers, +5 volts to other amplifiers and processing stages, and +24 volts to large signal and power driver stages, must be provided.
It will also be understood that a balanced (plus and minus DC) voltage supply, namely, a supply which delivers two voltages of equal magnitude but of opposite sign, is required in equipment capable of receiving and/or transmitting digital data from or to other data processing equipment wherein the value of the bits of data handled by such equipment ("0" or "1") corresponds to the polarity of the bit signals; e.g., RS-232C interface applications.
The known prior power supplies in electronic equipment of the above kind which require multiple levels of DC supply voltages, require either a number of separate power transformers each corresponding to a different one of the supply voltages, or a power transformer having numerous secondary windings and/or taps each of which is connected to an associated rectifier/filter stage for supplying one of the required DC supply voltages in the equipment. Since each of the transformers has to withstand certain minimum load current demands at the associated supply voltage, it is relatively costly to provide multiple power transformers each of sufficient current handling capability, or even a single high-power rated transformer with multiple secondary winding taps.
Much of the cost incurred in the latter case; i.e., a multi-tapped secondary winding, is due to the fact that custom transformer design is ordinarily called for to ensure that the taps are connected to the secondary winding at such locations as to enable the various rectifier/filter and regulator stages in the power supply to maintain the DC supply voltages constant under load.